2.1 Field of the Technology
The present technology relates to one or more of the detection, diagnosis, treatment, prevention and amelioration of respiratory-related disorders. In particular, the present technology relates to medical devices or apparatus, and their use.
2.2 Description of the Related Art
Human Respiratory System
The respiratory system of the body facilitates gas exchange. The nose and mouth form the entrance to the airways of a patient.
The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lung is gas exchange, allowing oxygen to move from the air into the venous blood and carbon dioxide to move out. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alleviated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. See West, Respiratory Physiology—the essentials.
A range of respiratory disorders exist.
Obstructive Sleep Apnea (OSA), a form of Sleep Disordered Breathing (SDB), is characterized by occlusion or obstruction of the upper air passage during sleep. It results from a combination of an abnormally small upper airway and the normal loss of muscle tone in the region of the tongue, soft palate and posterior oropharyngeal wall during sleep. The condition causes the affected patient to stop breathing for periods typically of 30 to 120 seconds duration, sometimes 200 to 300 times per night. It often causes excessive daytime somnolence, and it may cause cardiovascular disease and brain damage. The syndrome is a common disorder, particularly in middle aged overweight males, although a person affected may have no awareness of the problem. See U.S. Pat. No. 4,944,310 (Sullivan).
Cheyne-Stokes Respiration (CSR) is a disorder of a patient's respiratory controller in which there are rhythmic alternating periods of waxing and waning ventilation, causing repetitive de-oxygenation and re-oxygenation of the arterial blood. It is possible that CSR is harmful because of the repetitive hypoxia. In some patients CSR is associated with repetitive arousal from sleep, which causes severe sleep disruption, increased sympathetic activity, and increased afterload. See U.S. Pat. No. 6,532,959 (Berthon-Jones).
Obesity Hyperventilation Syndrome (OHS) is defined as the combination of severe obesity and awake chronic hypercapnia, in the absence of other known causes for hypoventilation. Symptoms include dyspnea, morning headache and excessive daytime sleepiness.
Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a group of lower airway diseases that have certain characteristics in common. These include increased resistance to air movement, extended expiratory phase of respiration, and loss of the normal elasticity of the lung. Examples of COPD are emphysema and chronic bronchitis. COPD is caused by chronic tobacco smoking (primary risk factor), occupational exposures, air pollution and genetic factors. Symptoms include: dyspnea on exertion, chronic cough and sputum production.
Neuromuscular Disease (NMD) is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles either directly via intrinsic muscle pathology, or indirectly via nerve pathology. Some NMD patients are characterised by progressive muscular impairment leading to loss of ambulation, being wheelchair-bound, swallowing difficulties, respiratory muscle weakness and, eventually, death from respiratory failure. Neuromuscular disorders can be divided into rapidly progressive and slowly progressive: (i) Rapidly progressive disorders: Characterised by muscle impairment that worsens over months and results in death within a few years (e.g. Amyotrophic lateral sclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers); (ii) Variable or slowly progressive disorders: Characterised by muscle impairment that worsens over years and only mildly reduces life expectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic muscular dystrophy). Symptoms of respiratory failure in NMD include: increasing generalised weakness, dysphagia, dyspnea on exertion and at rest, fatigue, sleepiness, morning headache, and difficulties with concentration and mood changes.
Chest wall disorders are a group of thoracic deformities that result in inefficient coupling between the respiratory muscles and the thoracic cage. The disorders are usually characterised by a restrictive defect and share the potential of long term hypercapnic respiratory failure. Scoliosis and/or kyphoscoliosis may cause severe respiratory failure. Symptoms of respiratory failure include: dyspnea on exertion, peripheral oedema, orthopnea, repeated chest infections, morning headaches, fatigue, poor sleep quality and loss of appetite.
Otherwise healthy individuals may take advantage of systems and devices to prevent respiratory disorders from arising.
2.2.1 Therapy
Nasal Continuous Positive Airway Pressure (CPAP) therapy has been used to treat Obstructive Sleep Apnea (OSA). The hypothesis is that continuous positive airway pressure acts as a pneumatic splint and may prevent upper airway occlusion by pushing the soft palate and tongue forward and away from the posterior oropharyngeal wall.
Non-invasive ventilation (NIV) provides ventilator support to a patient through the upper airways to assist the patient in taking a full breath and/or maintain adequate oxygen levels in the body. The ventilator support is provided via a patient interface. NIV has been used to treat CSR, OHS, COPD, MD and Chest Wall disorders.
Invasive ventilation (IV) provides ventilatory support to patients that are no longer able to effectively breathe themselves and is provided using a tracheostomy tube.
Ventilators may control the timing and pressure of breaths pumped into the patient, and monitor the breaths taken by the patient. The methods of control and monitoring patients typically include volume-cycled and pressure-cycled methods. The volume-cycled methods may include among others. Pressure-Regulated Volume Control (PRVC), Volume Ventilation (VV), and Volume Controlled Continuous Mandatory Ventilation (VC-CMV) techniques. The pressure-cycled methods may involve, among others. Assist Control (AC). Synchronized Intermittent Mandatory Ventilation (SIMV), Controlled Mechanical Ventilation (CMV), Pressure Support Ventilation (PSV), Continuous Positive Airway Pressure (CPAP), or Positive End Expiratory Pressure (PEEP) techniques.
2.2.2 Systems
A treatment system may comprise a Respiratory Pressure Therapy Device (RPT device), an air circuit, a humidifier, a patient interface, and data management.
2.2.3 Patient Interface
A patient interface may be used to interface respiratory equipment to its user, for example by providing a flow of air. The flow of air may be provided via a mask to the nose and/or mouth, or via a tracheostomy tube to the trachea of the user. Depending upon the therapy to be applied, the patient interface may form a seal, e.g. with a face region of the patient, to facilitate the delivery of air at a pressure at sufficient variance with ambient pressure to effect therapy, e.g. a positive pressure of about 10 cmH2O. For other forms of therapy, such as the delivery of oxygen, the patient interface may not include a seal sufficient to facilitate delivery to the airways of a supply of air at a positive pressure of about 10 cmH2O. Some masks suffer from being one or more of obtrusive, aesthetically undesirable, costly, poorly fitting, difficult to use, and uncomfortable especially when worn for long periods of time or when a patient is unfamiliar with a system. Masks designed solely for aviators as part of personal protection equipment or for the administration of anaesthetics may be tolerable for their original application, but nevertheless be undesirably uncomfortable to be worn for extended periods, for example, while sleeping or throughout the day.
2.2.4 Respiratory Pressure Therapy (RPT) device
One known RPT device used for treating sleep disordered breathing is the S9 Sleep Therapy System, manufactured by ResMed. Another example of an RPT device is a ventilator. Ventilators such as the ResMed Stellar™ Series of Adult and Paediatric Ventilators may provide support for invasive and non-invasive non-dependent ventilation for a range of patients for treating a number of conditions such as but not limited to NMD, OHS and COPD.
The ResMed Elisée™ 150 ventilator and ResMed VS III™ ventilator may provide support for invasive and non-invasive dependent ventilation suitable for adult or paediatric patients for treating a number of conditions. These ventilators provide volumetric and barometric ventilation modes with a single or double limb circuit.
RPT devices typically comprise a pressure generator, such as a motor-driven blower or a compressed gas reservoir, and are configured to supply a flow of air to the airway of a patient. In some cases, the flow of air may be supplied to the airway of the patient at positive pressure. The outlet of the RPT device is connected via an air circuit to a patient interface such as those described above.
RPT devices typically also include an inlet filter, various sensors and a microprocessor-based controller. A blower may include a servo-controlled motor, a volute and an impeller. In some cases a brake for the motor may be implemented to more rapidly reduce the speed of the blower so as to overcome the inertia of the motor and impeller. The braking can permit the blower to more rapidly achieve a lower pressure condition in time for synchronization with expiration despite the inertia. In some cases the pressure generator may also include a valve capable of discharging generated air to atmosphere as a means for altering the pressure delivered to the patient as an alternative to motor speed control. The sensors measure, amongst other things, motor speed, mass flow rate and outlet pressure, such as with a pressure transducer or the like. The controller may include data storage capacity with or without integrated data retrieval and display functions.
Table of noise output levels of prior RPT devices (one specimen only, measured using test method specified in ISO3744 in CPAP mode at 10 cmH2O).
A-weighted sound powerYearRPT Device namelevel dB(A)(approx.)C-Series Tango31.92007C-Series Tango with Humidifier33.12007S8 Escape II30.52005S8 Escape II with H4i Humidifier31.12005S9 AutoSet26.52010S9 AutoSet with H5i Humidifier28.620102.2.5 Humidifier
Delivery of a flow of air to a patient's airways without humidification may cause drying of the airways. Medical humidifiers are used to increase humidity and/or temperature of the flow of air in relation to ambient air when required, typically where the patient may be asleep or resting (e.g. at a hospital). As a result, a medical humidifier may be small for bedside placement, and may be configured to humidify and/or heat the flow of air delivered to the patient without humidifying and/or heating the patient's surroundings. Room-based systems (e.g. a sauna, an air conditioner, an evaporative cooler), for example, may also humidify and/or heat air that is breathed in by the patient, however they would do so by humidifying and/or heating the entire room, which may cause discomfort to the occupants.
The use of a humidifier with a RPT device and the patient interface produces humidified air that minimizes drying of the nasal mucosa and increases patient airway comfort. In addition in cooler climates, warm air applied generally to the face area in and about the patient interface is more comfortable than cold air.
Respiratory humidifiers are available in many forms and may be a standalone device that is coupled to a RPT device via an air conduit, is integrated with the RPT device or configured to be directly coupled to the relevant RPT device. While known passive humidifiers can provide some relief, generally a heated humidifier may be used to provide sufficient humidity and temperature to the air so that the patient will be comfortable. Humidifiers typically comprise a water reservoir or tub having a capacity of several hundred milliliters (ml), a heating element for heating the water in the reservoir, a control to enable the level of humidification to be varied, an air inlet to receive air from the RPT device, and an air outlet adapted to be connected to an air circuit that delivers the humidified air to the patient interface.
Heated passover humidification is one common form of humidification used with a RPT device. In such humidifiers the heating element may be incorporated in a heater plate which sits under, and is in thermal contact with, the water tub. Thus, heat is transferred from the heater plate to the water reservoir primarily by conduction. The air flow from the RPT device passes over the heated water in the water tub resulting in water vapour being taken up by the air flow. The ResMed H4i™ and H5i™ Humidifiers are examples of such heated passover humidifiers that are used in combination with ResMed S8 and S9 CPAP devices respectively.
Other humidifiers may also be used such as a bubble or diffuser humidifier, a jet humidifier or a wicking humidifier. In a bubble or diffuser humidifier the air is conducted below the surface of the water and allowed to bubble back to the top. A jet humidifier produces an aerosol of water and baffles or filters may be used so that the particles are either removed or evaporated before leaving the humidifier. A wicking humidifier uses a water absorbing material, such as sponge or paper, to absorb water by capillary action. The water absorbing material is placed within or adjacent at least a portion of the air flow path to allow evaporation of the water in the absorbing material to be taken up into the air flow.
An alternative form of humidification is provided by the ResMed HumiCare™ D900 humidifier that uses a CounterStream™ technology that directs the air flow over a large surface area in a first direction whilst supplying heated water to the large surface area in a second opposite direction. The ResMed HumiCare™ D900 humidifier may be used with a range of invasive and non-invasive ventilators.
Typically, the heating element is incorporated in a heater plate which sits under, and is in thermal contact with, the water tub. Thus, heat is transferred from the heater plate to the water reservoir primarily by conduction.